A rubber hose is used as a component for automobiles or another industrial component. For example, a heat resistant air rubber hose is used for a turbo charger of a diesel automobile, etc. A heat resistant air rubber hose installed in a turbo charger has a role to supply to an engine, high temperature/high pressure compressed gas which is compressed in the turbo charger. In such compressed gas, a high temperature mist of a fuel, an engine oil, etc. discharged from the engine is also contained. Therefore, the heat resistant air rubber hose is required to have a high heat resistance, a chemical resistance, an oil resistance and a pressure resistance.
Heretofore, an acrylic rubber has been used for a heat resistant air rubber hose. In recent years, a demand for the heat resistance of the heat resistant air rubber hose has become severe, and an acrylic rubber is insufficient to satisfy such a required property. As a material which satisfies such a required property, a fluorinated rubber is available. The fluorinated rubber is excellent in properties such as the heat resistance, the chemical resistance, the oil resistance and the pressure resistance, and thereby the fluorinated rubber is suitable as a material for the heat resistant air rubber hose. However, since the fluorinated rubber is expensive, there is a problem such that the cost for the heat resistant air rubber hose becomes high.
Accordingly, it has been tried to reduce the cost for a rubber hose by forming a laminate of a fluorinated rubber and an inexpensive material such as an acrylic rubber.
Patent Document 1 discloses a laminated rubber hose comprising an inner layer made of a vinylidene fluoride-hexafluoropropylene elastic copolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene elastic copolymer, a tetrafluoroethylene-propylene elastic copolymer or a tetrafluoroethylene-vinylidene fluoride-propylene elastic copolymer, and an outer layer made of an acrylic rubber, which are co-vulcanized.
However, in general, a fluorinated rubber is poor in affinity with another rubber material such as an acrylic rubber, and in the laminated rubber hose of Patent Document 1, the adhesive property of the fluorinated rubber layer and the acrylic rubber layer is insufficient. Particularly, under high temperature conditions, they tend to peel at their bonding interface.
Here, as one of fluorinated rubber compositions, there is an acrylic rubber/fluorinated rubber composition having particles of a crosslinked acrylic rubber dispersed in a continuous phase of a fluorinated rubber. The acrylic rubber/fluorinated rubber composition is molded and crosslinked so as to be used as a molded product such as a part for automobiles or an industrial part.
Patent Document 2 discloses a process for producing an acrylic rubber/fluorinated rubber composition having particles of a crosslinked acrylic rubber dispersed in a continuous phase of a fluorinated rubber, which comprises blending a fluorinated rubber, an acrylic rubber, a third elastomer co-crosslinkable with both the fluorinated rubber and the acrylic rubber, and a crosslinking agent for an acrylic rubber, and dynamic-crosslinking them, while applying shearing deformation.
Further, Patent Document 3 discloses a production process which comprises mixing in a latex state, a latex of an inter-crosslinked epoxy group-containing acrylic rubber having a gel content of at least 80 wt % and a latex of a fluorinated rubber, followed by co-coagulating the obtained mixed latex.
However, in the process of Patent Document 2, it is necessary to carry out the dynamic-crosslinking usually at a high temperature of at least 200° C., and thereby the productivity is poor. Further, in such a process, it is necessary to add a third elastomer, and if the dynamic-crosslinking is carried out without adding the third elastomer, an exfoliation results at the interface between the fluorinated rubber phase and the acrylic rubber particles, and thereby the mechanical property is insufficient.
Further, in the process of Patent Document 3, latexes made of different materials are mixed with each other. However, in a case where latexes made of different materials are to be mixed on a commercial scale, contamination to conventional products is concerned, and therefore, it is necessary to spend high cost for facilities, for example for building a new coagulation tank, whereby the cost tends to increase, and such a process is not industrially appropriate.
Further, in Patent Documents 2 and 3, no study is made with respect to an interlayer-adhesion at the time of laminating a fluorinated rubber.